The present invention is used with devices known as "smart two-wire process transmitters" that must be set up or configured in one of a multitude of modes, depending on the application. Signal transmitters accept one form of various low-level signals from a sensor or transducer and convert such signals to a standard form known as a 4-to-20-mA current loop. Such transmitters are used in the process industries and are used for measuring temperature, pressure, flow, level and various other variables associated with the process (hereinafter referred to as a process variable).
Generally, to measure each of these different process variables a different design transmitter is required. Transmitters that are designed using classical analog circuit technology even require different models of transmitters depending on the range of the measured variable. Typically, a transmitter receives a low-level (microvolt and millivolt level) signal from thermocouples, pressure, flow, level and other sensors; converts these low-level signals near the location of the sensor to a suitable high-level signal, and transmits such high-level signal to a remote location within a process plant, such as the control room. Alternatively, the signals output can also be transmitted to a process control system associated with industrial process, that is used to monitor, collect and manipulate the process variables.
In recent years "smart" process transmitters have been introduced. These devices are distinguished from their analog predecessors by utilizing one or more microprocessors for their operation. These so-called smart transmitters easily implement digital communications with a digital terminal or other digital computer. All current smart two-wire transmitters offer some form of digital communication with either local terminals or to a process control systems central computer. Additionally, some smart two-wire transmitters include internally-stored programming instruction that manipulate in one form or another the process variables received from the sensors. This manipulation can be as simple as selecting a sensor or as complicated as deriving and transmitting to a process control system an output signal indicative of the product of an algorithmic calculation using the process values sensed.
Presently known smart transmitter's operating and configuration programs are normally stored in a Read Only Memory (ROM). The operating and configuration instructions loaded in the ROM characterize the process transmitter and defines its functionality. The term characterize is used in this invention to describe the character of the device. Or that which operationally distinguishes the process transmitter from other process transmitters, such as a transmitter that senses and transmits pressure signals from a transmitter that senses and transmits flow signals. The term functionality is defined as the operating behavior of the process transmitter within its character role, such as in a temperature transmitter, the frequency that a temperature sensor is polled by the transmitter to gather process variable data, or in a multi-variable transmitter, the algorithmic routines used to derive and calculate a manipulated variable from one or more process variables sensed and collected. The ROM is programmed and assembled into the transmitter at the time of manufacture. In order to change a transmitter's character and functionality, the transmitter has to be removed from the process, opened, and the ROM physically removed and replaced with a new ROM.
This has many undesirable consequences. First, the removal of the transmitter effectively stops the monitoring and collection of the variables associated with that portion of the process. If these process variables are critical to the product being produced, the loss of this information may necessitate the temporary shut-down of the manufacturing or industrial process. This may a have a negative economic impact on the manufacturer due to the loss of production and the cost of starting-up production again. Second, the opening of the transmitter and physical replacement of the ROM has inherent dangers in the potential damage to the electronic and electrical components and circuits of the device. Static electrical discharges and undo mechanical strain and other dangers associated with physically handling sensitive low-power electrical devices can leave these devices non-functional, requiring replacement of the damaged circuits or devices or replacement of the entire transmitter.
An apparatus for configuring a smart transmitter is taught by U.S. Pat. No. 5,083,288, to Somlyody et al. This invention teaches an apparatus for configuring a smart transmitter that uses switches to configure the transmitter to perform various functions. The transmitter includes a program and an apparatus for cycling through the program to set various conditions, including a range of operation and selection of one of many possible remote sensors. The program includes two portions, each of which can be entered by a user-manipulated switch. Each portion of the program can be cycled through, and as selected portions of the program are reached, a selected parameter can be set into the microprocessor as a permanent operating condition. The set operating conditions can be set or reset at any time by cycling through the program in accordance with the set protocol.
The apparatus and method described above has limitations in that any configuration programs that changes the functionality of the device has to be loaded initially into the transmitter at the time of manufacture, thereby limiting its functionality to the operating characteristics that have been previously loaded. Additionally, there are no provisions in the initial programming that can change the character of the transmitter.